The effects of a warming of the Earth's temperature by even two degrees Celsius could put up to 400 million people at risk of hunger and leave up to two billion lacking enough water resources. The world's governments have set themselves a goal of keeping warming below that two-degree mark. The costs of living in a warmer climate make it critical that governments act now to reduce greenhouse-gas emissions blamed for causing the warming, the World Bank said.

"All agree that it's better to adopt mitigation measures now rather than to adopt adaptation later," World Bank chief economist Justin Lin told reporters in Istanbul, where the World Bank and International Monetary Fund are holding their annual meetings. Developing countries will bear the brunt of global warming: Between 75 per cent and 80 per cent of its effects will hit the developing world, according to a World Bank report released last month.

The World Bank estimates the world will suffer a one percent drop in economic output because of climate change, with minimal effects for advanced countries, compared to a drop of 4-5 per cent for Africa and South Asia. That means wealthy economies should help developing countries adapt, Lin said. Financing for developing countries remains a key dispute for a new global climate treaty, which world governments hope to hammer out by a UN summit in Copenhagen in December.